Steam Engines
As an amusement, Greek mathematician and engineer Hero of Alexandria made a simple bladeless radial steam turbine called an aeolipile in the 1st century CE.
The aeolipile was a vessel with pipes running into it, sitting in a basin of water which is heated, providing the steam source. The aeolipile had a stream release in the form of 2 nozzles (tipjets). When the vessel was pressurized, steam vented from the tipjets, generating thrust via the rocket principle, making the vessel rotate.
Italian engineer and architect Giovanni Branca described an impulse steam turbine in his 1629 book Le Machine. It bore no relation to later applications of steam power and was not much of an advance over the aeolipile. Branca’s turbine was one of many different mechanical inventions that he wrote of, some of which he himself had envisioned. English historian Alex Keller later commented that Branca’s book was of “armchair inventions which seldom ever had any 3-dimensional working counterparts.”
In 1678, Jean de Hautefeuille proposed using a piston in a heat engine powered by gunpowder. 2 years later, Christiaan Huygens and French inventor Denis Papin built a prototype.
Heat engines under steam power were first meaningfully employed for mining. As demand for coal and metals grew the desire to dig deeper grew stronger. Flooding from going below the water table was the chief obstacle.
English engineer Thomas Savery patented a steam pump in 1698 which he called “The Miner’s Friend.” A few were tried in the following decade, mostly in Cornish tin mines. They had several defects, among them a tendency to explode.
By trial-and-error tinkering English ironmonger and lay preacher Thomas Newcomen succeeded in making a workable steam pump in 1712. Newcomen had a business that specialized in designing, manufacturing, and peddling tools to the mining industry. Newcomen’s contraption combined innovations by Savery and Papin, who had created the steam digester, a forerunner of the pressure cooker.
Though by no means efficient or especially reliable, the Newcomen steam pump was commercially viable for 75 years, as was Savery’s less-expensive steam engine. Their use spread throughout Britain and continental Europe. Then these pumps were replaced by a superior steam engine, designed by Scottish mechanical engineer and chemist James Watt, who began studying steam engines in the early 1860s.
Watt concluded that Newcomen’s engine wasted 80% of the steam, as steam was used to heat the cylinder rather than providing motive force. Taking Newcomen’s engine as a baseline, Watt made numerous improvements in design and materials, resulting in his own steam engine in 1781. Watt’s tireless dedication resulted in technology that enabled the widespread use of stationary steam engines.
At the time, the power of steam engines was limited by low pressure, cylinder displacement, condenser capacity, and the rates of combustion and evaporation. Efficiency was constrained by the relatively low temperature differential on either side of a piston.
This meant that a Watt engine had to be quite sizable to produce a useful amount of power. They were therefore expensive to build and install.
As the 18th century unfolded the call was for higher pressures. Watt strongly resisted this. Watt mistrusted the materials technology of the day, especially boilers being able to withstand high pressure. So, Watt used his patent monopoly to prevent others from building high-pressure engines and using them in vehicles.
Watts’ reservations did not apply in the US, where his patent power did not reach. Several advocates of “strong steam” built high-pressure engines. One was American engineer and businessman Oliver Evans. A pioneer in cylindrical boilers, his radical designs were criticized by other engineers.
Evans did suffer several serious boiler explosions, validating Watts qualms. But Evans persisted, and introduced high-pressure steam engines to the riverboat trade on the Mississippi.
English mining engineer Richard Trevithick was the son of a mine captain. He grew up watching steam engines pump water from deep mines in Cornwall. In 1799, Trevithick was first to make a successful high-pressure steam engine. Unlike the more insouciant Evans, Trevithick worked incrementally: experimentally finding out what worked and what did not.
Trevithick had his first patent for a high-pressure steam engine in 1802, having built both stationary and vehicular engines.
Trevithick’s work was not without mishap. In 1803, one of his stationary pumping engines exploded, killing 4 men. Trevithick’s response was to incorporate safety valves and other measures to warn of impending danger.
American mechanical engineer George Henry Corliss developed a reliable stationary steam engine which he patented in 1849. His work became recognized as the greatest advance in steam power since Watt.
One of the final developments in stationary steam engines was running them at high speed: several hundred rpm (revolutions per minute), which was a necessity for electricity generation. As a turbine generates rotary motion, a turbine is particularly suited to drive an electrical generator.
In 1882, Swedish engineer Gustaf de Laval designed an impulse steam engine that subjected the turbine to severe centrifugal forces. This limited output due to the weakness of materials available at the time.
Appreciating the practical flaws in Laval’s turbine design, Anglo Irish engineer Charles Parsons invented the modern steam turbine in 1884. He immediately employed it to drive an electrical generator he had designed.
It seemed to me that moderate surface velocities and speeds of rotation were essential if the turbine motor was to receive general acceptance as a prime mover. I therefore decided to split up the fall in pressure of the steam into small fractional expansions over a large number of turbines in series, so that the velocity of the steam nowhere should be great. I was also anxious to avoid the well-known cutting action on metal of steam at high velocity. ~ Charles Parsons
Parsons’ steam turbine made plentiful, cheap electricity possible. It also revolutionized marine transport and naval warfare.
~85% of electricity generated worldwide today comes via steam turbines, including those powered by coal, geothermal, solar, gas, and atomic decay. The different energy inputs go to the same end: to boil water.
The energy conversion efficiency of modern steam turbine power plants is typically 33–45%: the rest of the energy leaves the power plant as waste heat.
